The present invention relate to an X-ray CT (computed tomography) apparatus, and more particularly to an X-ray CT apparatus using a multi-slice multi-channel X-ray detector.
An X-ray CT apparatus is so configured as to reconstruct an image on the basis of X-ray detected data obtained by scanning a subject with an X-ray source and an X-ray detector that rotate as opposed to each other. When a multi-slice multi-channel X-ray detector is to be used as the X-ray detector, the coverage in the body axis direction of the subject becomes greater, and therefore the efficiency of scanning is enhanced (see Patent Document 1 for instance).
[Patent Document 1] JP-A No. 2005-324052
The coverage in the body axis direction of the subject is given by the following equation. Hereinafter the body axis direction may be sometimes referred to as the z direction.c=n×d 
Here, n is the number of slices of the X-ray detector and d, the slice thickness per slice. The slice thickness d determines the spatial resolution in the z direction. The spatial resolution, given by 1/d, increases with a decrease in the slice thickness d. Hereinafter the spatial resolution may be sometimes referred to as simply the resolution.
Since the resolution 1/d and the coverage c are in a relationship of inverse proportion to each other where the number of slices n is constant, improving the resolution and improving the coverage cannot be compatible. Therefore, a multi-slice multi-channel X-ray detector is produced with emphasis placed on either the resolution or the coverage where the number of slices is given. An X-ray CT apparatus using such an X-ray detector cannot help being either a resolution-oriented X-ray CT apparatus or a coverage-oriented X-ray CT apparatus.
According to Patent Document 1 cited above, compatibility between the resolution orientation and the coverage orientation is sought by so configuring the X-ray detector as to have thinner parts and thicker parts in slice thickness in all the channels, but an X-ray detector having thinner parts and thicker parts in slice thickness in all the channels costs higher.